Epidemiology and magnetic resonance imaging-based diagnostics of knee injuries and anterior knee pain in young adults

(1)

Epidemiology and Magnetic Resonance

Imaging-Based Diagnostics of Knee Injuries

and Anterior Knee Pain in Young Adults

ACADEMIC DISSERTATION To be presented, with the permission of

the board of the School of Medicine of the University of Tampere, for public discussion in the Auditorium of Finn-Medi 5, Biokatu 12, Tampere, on August 23rd, 2012, at 12 o’clock.

(2)

Reviewed by

Docent Arsi Harilainen University of Helsinki Finland

Docent Juhana Leppilahti University of Oulu Finland Distribution Bookshop TAJU P.O. Box 617 33014 University of Tampere Finland Tel. +358 40 190 9800 Fax +358 3 3551 7685 taju@uta.fi www.uta.fi/taju http://granum.uta.fi Cover design by Mikko Reinikka Taitto Sirpa Randell

Acta Universitatis Tamperensis 1753 ISBN 978-951-44-8876-4 (print) ISSN-L 1455-1616

ISSN 1455-1616

Acta Electronica Universitatis Tamperensis 1226 ISBN 978-951-44-8877-1 (pdf )

ISSN 1456-954X http://acta.uta.fi

Tampereen Yliopistopaino Oy – Juvenes Print Tampere 2012

University of Tampere, School of Medicine Centre for Military Medicine

Central Military Hospital, Department of Orthopedic Surgery Finland

Supervised by

Docent Harri Pihlajamäki University of Helsinki Finland

Docent Ville Mattila University of Tampere Finland

(3)

1 List of Original Publications

This thesis is based on the following original publications, which are referred to in the text by the Roman numerals I–IV:

I Kuikka, P. I., Kiuru, M. J., Niva, M. H., Kröger, H., Pihlajamäki, H. K. (2006). Sensitivity of routine 1.0-Tesla magnetic resonance imaging versus arthroscopy as gold standard in fresh traumatic chondral lesions of the knee in young adults. Arthroscopy, 22(10), 1033–1039.

II Kuikka, P. I., Sillanpää, P., Mattila, V. M., Niva, M. H., Pihlajamäki, H. K. (2009). Magnetic resonance imaging in acute traumatic and chronic meniscal tears of the knee: A diagnostic accuracy study in young adults. Am J Sports Med, 37(5), 1003– 1008.

III Pihlajamäki, H. K., Kuikka, P. I., Leppänen, V. V., Kiuru, M. J., Mattila, V. M. (2010). Reliability of clinical findings and magnetic resonance imaging for the diagnosis of chondromalacia patellae. J Bone Joint Surg Am, 92(4), 927–934. IV Kuikka, P. I., Pihlajamäki, H. K., Mattila, V.M. (2011). Knee injuries related to

sports in young adult males during military service – Incidence and risk factors. Scand J Med Sci Sports. Epub 2011 Oct 19.

Articles I–IV have been reprinted in this thesis with the permission from Elsevier (I), SAGE Publications (II), J Bone Joint Surg Am. (III) and Blackwell Munksgaard (IV).

(8)

2 Abbreviations

ACL = Anterior cruciate ligament AKP= Anterior knee pain BMI = Body mass index CI= Confidence Interval

CMP = Chondromalacia patellae CT = Computed tomography

ICRS = International Cartilage Repair Society LCL = Lateral collateral ligament

MCL = Medial collateral ligament MRI = Magnetic Resonance Imaging

NHDR = National hospital discharge register OR = Odds Ratio

PCL = Posterior cruciate ligament PFM = Patellofemoral malalignment PFPS = Patellofemoral pain syndrome SPGR = Spoiled gradient echo

T = Tesla

(9)

3 Tiivistelmä

Tämän väitöskirjan tarkoituksena on selvittää nuorten aikuisten miesten polvivammo-jen ilmaantuvuutta ja riskitekijöitä sekä magneettikuvauspainotteista diagnostiikkaa tuoreissa polven rustovaurioissa, nivelkierukan repeämissä ja polven etuosan kivussa.

Epidemiologisena aineistona tutkimuksessa olivat kaikki tutkimusajanjakson ai-kana varusmiespalveluksensa suorittaneet 18–30-vuotiaat miespuoliset varusmiehet (n=128 584). Altistumisaika oli 97 503 henkilövuotta. Pakollisen asevelvollisuuden vuoksi varusmiehet edustavat erittäin hyvin perustervettä nuorta aikuista miesväestöä Suomessa. Kaikki sairaalahoitoon johtaneet polvivammat tässä aineistossa selvitettiin kansallisen hoitoilmoitusrekisterin avulla. Polvivammoja käsiteltiin kokonaisuutena ja lisäksi jaoteltuina erillisiin diagnooseihin, joita olivat ristiside- ja sivusidevammat, ni-velkierukkarepeämät, traumaattiset rustovauriot ja polvilumpion sijoiltaanmenot. Tie-dot palveluskelpoisuusluokan muutoksista ja mahdollisesti polvivammoihin yhteydessä olevista riskitekijöistä saatiin puolustusvoimien sisäisistä rekistereistä.

Magneettikuvauksen diagnostista validiteettia tuoreissa rustovaurioissa sekä tuo-reissa ja vanhoissa nivelkierukkarepeämissä tutkittiin retrospektiivisesti. Aineistojen kaikille potilaille oli tehty magneettikuvaus ja artroskopia keskussotilassairaalassa nor-maalin kliinisen käytännön mukaisesti. Tuoreiden rustovaurioiden magneettikuvausta käsittelevään aineistoon otettiin mukaan 32 potilasta, joilla oli todettu artroskopiassa tuore traumaattinen rustovaurio. Potilaiden mediaani-ikä oli 19 vuotta (vaihteluväli 19–21).

Tuoreiden ja vanhojen nivelkierukkarepeämien magneettikuvausdiagnostiikkaa ver-tailevien aineistojen mukaanottokriteerit täytti 82 potilaista, joilla oli tuore polvivamma, ja 40 potilasta, joilla oli pidempikestoinen polviongelma. Potilaiden mediaani-ikä oli 20 vuotta (vaihteluväli 18–25).

Polven etuosan kipuun liittyvien oireiden ja statuslöydösten yhteyttä artroskoopsiin löydökartroskoopsiin tutkittiin prospektiivisesti 56 varusmiehen aineistossa. Kaikilla oli pi-dempiaikainen, vammaan liittymätön polven etuosan kiputila. Potilaiden mediaani-ikä oli 19.5 vuotta (vaihteluväli 18–25). Kaikille tutkimukseen valituille tehtiin magneetti-kuvaus ja artroskopia keskussotilassairaalassa.

Sairaalahoitoon johtaneiden polvivammojen ilmaantuvuus kokonaisuutena oli 11 potilasta 1000 henkilövuotta kohden [95 % luottamusväli (CI): 10.4–11.7]. Polvivammo-jen riskitekijöitä analysoitiin logistisella regressiolla. Merkittävimmät riskitekijät

(10)

polvi-vammoille olivat korkeampi ikä (OR 1.7; 95 % CI: 1.3–2.2) ja ylipaino (OR 1.6; 95 % CI: 1.03–2.5). Kirurginen toimenpide tehtiin kahdelle kolmasosalle kaikista sairaalassa hoidetuista potilaista ja pidempiaikainen haitta (palveluskelpoisuusluokan muutos) jäi yhdelle kolmasosalle potilaista.

Tuoreiden traumaattisten rustovaurioiden todentamisessa 1.0 Teslan magneetti-kuvauk sen sensitiivisyys oli alhainen. Sensitiivisyys oli riippuvainen rustovaurion syvyydestä, ollen pinnallisissa vaurioissa vain 17 %. Koko ruston syvyyden kattaville vaurioille sensitiivisyys oli hieman parempi, 57 %. Tulos tarkoittaa, että lähes puolet sy-vistä rustovaurioista jäi diagnosoimatta magneettikuvauksessa. Huolimatta normaalista magneettikuvauslöydöksestä saattaa artroskopia paljastaa korjaustoimenpiteisiin sovel-tuvia syviä rustovaurioita.

Tuoreiden ja vanhojen nivelkierukkarepeämien magneettikuvauksen diagnostisessa validiteetissa ei todettu merkittävää eroa. Tutkimustulokset antoivat myös viitteitä siitä, että polvinivelen turvotus tai veripolvi ei heikennä diagnostista validiteettia.

Polven etuosan kipua käsittelevässä 56 potilaan aineistossa todettiin polvilumpion rustovaurio 25 tapauksessa (45 %). Nivelkalvon poimu todettiin myös 25 polvessa, ni-velkierukan repeämä 4 polvessa, femorotibiaalinen rustovaurio neljässä polvessa ja nor-maali anatomia kuudessa polvessa. Polvilumpion takainen krepitaatio tai polvilumpion painamisesta provosoituva kipu ei lisännyt rustovaurioiden todennäköisyyttä potilail-la, joilla oli tyypilliset polven etuosan kiputilaan liittyvät oireet. Oireiden, löydösten ja polvilumpion rustovaurion asteen välillä ei todettu selkeää yhteyttä (p = 0.83). Tulokset tukevat aiempia havaintoja siitä, että polvilumpion rustovaurioita ei voida luotettavas-ti diagnosoida oireiden ja statuslöydösten perusteella. 1.0 Teslan magneetluotettavas-tikuvauksen sensitiivisyys oli alhainen luokan I rustovaurioille (13 %), mutta selkeästi parempi sy-vemmille rustovaurioille (83 %). Magneettikuvausta voidaankin käyttää diagnostisena apuvälineenä polvilumpion syvempien, mahdollisesti operatiivista hoitoa tarvitsevien rustovaurioiden diagnostiikassa.

(11)

4 Abstract

Knee injuries and anterior knee pain are frequently encountered and treated by orthopaedic surgeons and general practitioners in daily clinical practice. Knee injuries are most common in those under 30 years of age and especially in males. Accurate incidence rates of knee injuries requiring hospitalisation (i.e. inpatient care admission) in this high-risk subgroup, however, are not known. Also unclear are the roles of intrinsic modifiable factors, such as body mass index (BMI), weight, aerobic fitness, and muscular strength, as risk factors for knee injuries.

The epidemiologic section of this dissertation is based on population-based data among Finnish young adult male conscripts. Our aim was to determine the incidence and possible risk factors for knee injuries requiring inpatient care. Moreover, knee injuries were analysed by specified diagnosis (cruciate and collateral ligament tears, meniscal tears, traumatic chondral lesions, and patellar dislocations). The total number of Finnish male conscripts performing their compulsory military service during the study period was 128,584 and total exposure time was 97,503 person-years. Risk factor analyses were performed by logistic regression. The person-based incidence of inpatient care admissions for knee injury in general was 11 cases per 1000 person-years (95% confidence interval [CI]: 10.4–11.7). The most important risk factors were higher age (odds ratio [OR] 1.7; 95% CI: 1.3–2.2) and obesity (OR 1.6; 95% CI: 1.03–2.5). Two-thirds of all subjects admitted to inpatient care for knee injuries had surgery, and one-third had long-term notable disability.

The diagnostic section of this dissertation addresses three diagnostic challenges: fresh traumatic chondral lesions, fresh meniscal tears, and anterior knee pain (AKP). Study populations were based on conscripts treated at the Central Military Hospital in Helsinki, Finland. Arthroscopic results served as the gold standard for calculating the sensitivity, specificity, and accuracy of magnetic resonance imaging (MRI) findings.

The validity of MRI for fresh traumatic chondral lesions and for fresh vs. old meniscal tears was studied retrospectively. Study populations comprised young adult conscripts in whom both knee MRI and arthroscopy were performed at the Central Military Hospital. In the first sample, 32 patients, ranging in age from 19 to 21 years (median, 19 years), with arthroscopically proven fresh traumatic chondral lesions of the knee met the inclusion criteria.

(12)

In the samples used for comparing MRI validity in fresh traumatic and old meniscal tears, 82 patients, ranging in age from 18 to 25 (median, 20 years) met the inclusion criteria with acute knee trauma (MRI within 30 days from trauma) and 40 patients with chronic knee symptoms (symptoms lasting over 6 months before MRI).

Diagnostic studies revealed that routine clinical use of 1.0 Tesla (T) MRI has poor sensitivity (36%) for detecting fresh traumatic articular cartilage lesions. Sensitivity was associated with the lesion grade and was only 17% for superficial lesions and moderately better, 57%, for full-thickness lesions. Thus, almost half of the full-thickness cartilage lesions remained undiagnosed following preoperative MRI. Despite negative MRI findings, arthroscopy may reveal lesions amenable to cartilage repair procedures.

The diagnostic validity of MRI for meniscal tears in acute knee trauma and in knee symptoms lasting over 6 months in young adults was similar. This study also suggests that effusion and haemarthrosis are not associated with the diagnostic validity of MRI for meniscal tears.

The association between the clinical symptoms and arthroscopic findings, and the role of MRI in AKP were studied prospectively. Fifty-six young adult conscripts (median age, 19.5 years) with AKP were prospectively selected for the study and MRI of the knee followed by arthroscopy was performed at the Central Military Hospital in Finland.

Arthroscopy conﬁrmed the presence of patellar chondral lesions in 25 (45%) of 56 knees of patients with AKP. Synovial plicae were as common a finding as patellar chondral lesions and was present in 25 knees. Normal anatomy was observed in only six knees. The presence of retropatellar crepitus or pain on manipulation of the patella was not associated with a higher proportion of patellar chondral lesions in patients with typical clinical AKP symptoms. The severity of patellar chondral lesions observed at arthroscopy was not associated with clinical symptoms of AKP syndrome (p = 0.83). This data supports earlier reports that patellar chondral lesions cannot be distinguished from other causes of AKP based on clinical symptoms and physical examination signs. The routine MRI protocol used for patients with AKP showed a sensitivity of only 13% for superficial patellar chondral lesions. For more severe lesions, the sensitivity was substantially higher, 83%, and 1.0T MRI may be considered a sensitive diagnostic tool in these cases.

(13)

5 Introduction

Injuries are the major cause of morbidity in young adults in Finland (Koskinen, 2005; Haikonen & Lounamaa, 2010). Sports injuries are the most common type of injury and young men in particular are a clear high-risk subgroup (Heiskanen, Sirén, et al., 2004; Parkkari, Kannus, et al., 2004; Haikonen & Lounamaa, 2010). Knee injuries comprise a significant portion of all sport and leisure time injuries (Haikonen & Lounamaa, 2010; Majewski, et al., 2006; Parkkari, et al., 2004). Knee injuries are a major cause of pain and disability in individuals and they are also a public health concern due to the costs associated with health care, work disability, and incapacitation. Population-based studies of the incidence and risk factors of knee injuries in young adult populations, however, are sparse. This information is essential because health differences during young adulthood may predict greater differences in health at an older age. Young adulthood is a critical age to target intervention programs because health habits are usually stabilising during that age period (Koskinen, 2005). Preventive strategies for knee injuries can only be utilised if their risk factors are known.

Valid diagnostics of knee injuries are critical for choosing the appropriate treatment methods and avoiding unnecessary treatments. Knee injury diagnostics are based on obtaining an accurate history and physical examination. Imaging modalities such as MRI can be performed when the diagnosis remains unclear after examination by a physician and analysis of plain radiographs. MRI became clinically available in the 1980s (Rappeport, et al., 1996), and is frequently used for diagnosing knee pathologies. Today, MRI of the knee joint is routine practice for the detection of trauma-related lesions, and is considered a sensitive and specific diagnostic method for evaluating meniscus and ligament injuries (Crawford, et al., 2007; Fischer, et al., 1991; Mackenzie, et al., 1996; Oei, et al., 2003; Rappeport, et al., 1996). Lower diagnostic validity is reported, however, when only acute knee injuries are included in the study (Lundberg, et al., 1996). Whether this is due to properties associated with acutely injured knees, such as haemarthrosis or catabolic processes of the meniscal tissue, or to varying methodologies and populations between studies, however, is unclear. There are no studies comparing the diagnostic validity of MRI for fresh and old meniscal lesions in an equivalent population with similar imaging methods.

Most previous studies of the diagnostic value of MRI for chondral lesions have focused on older populations in which the prevalence of osteoarthritis is high (Bredella,

(14)

et al., 1999; Disler, et al., 1996; Felson, 1988; Handelberg, et al., 1990; Hodler, et al., 1992; Potter, et al., 1998; Recht, et al., 1993; Riel, et al., 1999). MRI sensitivity varies widely between these studies (0%–100%) (Handelberg, et al., 1990; Munk, et al., 1998; Spiers, et al., 1993) and continues to be challenging (Figueroa, et al., 2007; von Engelhardt, et al., 2007). It remains unclear whether fresh traumatic chondral lesions of the knee in young adults can be diagnosed preoperatively by the routine MRI protocols used for overall knee examination.

AKP is one of the most common knee complaints in young adults. The pathophysiology behind AKP is poorly known and controversial. Patellar chondral lesions (chondromalacia patellae, CMP) was previously thought to be the reason for AKP, but this has been called into question because not all patients with AKP have patellar chondral lesions (Leslie & Bentley, 1978). According to the recently proposed tissue homeostasis theory, increased loading of the patellofemoral joint leads to a loss of tissue homeostasis in the surrounding innervated tissues, which causes the pain. Only in the most severe cases is loss of tissue homeostasis characterized by macrostructural damage such as chondral lesions (Dye, 2005). The widely accepted patellofemoral malalignment (PFM) theory is complementary to the tissue homeostasis theory. Patellofemoral malalignment may cause increased loading to the patellofemoral joint, which leads to a loss of tissue homeostasis (Sanchis-Alfonso, Vicente, 2011).

Further, the association between clinical symptoms and arthroscopic findings in AKP is not clear. Whether MRI can confirm possible patellar chondral lesions as an underlying cause of AKP is also uncertain, even if cartilage-specific sequences such as axial T1-weighted three-dimensional (3D) spoiled gradient echo (SPGR) is included in the routine knee evaluation protocol (Disler, et al., 1996; Gagliardi, et al., 1994; von Engelhardt, et al., 2007).

A reliable diagnosis of possible articular cartilage lesions as well as many other knee pathologies can be reached by arthroscopy, which allows for a direct view of the patellofemoral joint (Casscells, 1971; Figueroa, et al., 2007). Arthroscopic examination and treatment of the knee, however, also has some potential disadvantages. Because the arthroscopy procedure is invasive, it may lead to work disability, pain, and stress for the patient, and it is also associated with risks related to anaesthesia and surgery. Furthermore, unnecessary arthroscopies consume already-limited health care resources. In cases in which no surgically treatable lesion is found, arthroscopy can be considered an unnecessary diagnostic method and should be avoided. Valid preoperative diagnostics of chondral lesions are especially important in the young adult population. Within the last two decades, new treatment methods for chondral lesions, such as autologous chondrocyte implantation, have evolved and their results are generally moderate to good with a follow-up of a few years (Brittberg, et al., 1994; Gomoll, et al., 2010; Peterson, et al., 2002). These methods are especially useful for young adults with traumatic chondral lesions (Gomoll, et al., 2010; Kiviranta & Vasara, 2004; Peterson, et al., 2002; Vasara, et al., 2006). These

(15)

advanced surgical procedures are available at only a few hospitals in Finland (Vasara, et al., 2006). Valid, noninvasive diagnostic methods for deep symptomatic chondral lesions could help to choose the appropriate cartilage repair procedure.

(16)

6 Review of the Literature

6.1 Health Problems in Young Adults in Finland

The results of the Health 2000 Survey (Koskinen, 2005) conducted to evaluate the health of 18 to 29-year-old Finnish young adults indicated that young adults in Finland are generally rather healthy. For example cardiovascular diseases, diabetes, permanent injuries and severe disabilities are relatively rare in this age group.

Injuries are the major cause of morbidity in young adults in Finland as well as internationally (Haikonen & Lounamaa, 2010; Heiskanen, et al., 2004; Jones & Knapik, 1999; Parkkari, et al., 2004). In military populations, injuries can cause 10 times more limited duty days than illnesses (Jones & Knapik, 1999). In the Health 2000 Survey, 9% of the 18 to 29 year-old males and 4% of the females reported some permanent injury (Koskinen, 2005). Several studies demonstrated that sports injuries are the most common injury type in Finland, especially in younger people (Haikonen & Lounamaa, 2010; Heiskanen, et al., 2004; Parkkari, et al., 2004; Peltonen, et al., 2008) In a national victimisation survey, the incidence of sports injuries in the 15 to 24-year age group was 178 cases/1000 persons per year in 2009 (Haikonen & Lounamaa, 2010). Sports injuries were followed by injuries at home (90/1000 persons per year), at work (70/1000 persons per year), traffic-related (50/1000 persons per year), and during other leisure-time activities (30/1000 persons per year). Sports and traffic-related injuries were most common in the younger age groups, and clearly decreased with increasing age. Young men are especially a clear high-risk subgroup. Men aged 15 to 25 had 204 sports-related injuries per 1000 persons in 2009 and women in this age group reported 155 sports-related injuries per 1000 persons. The higher incidence rates in young persons may be due to more intensive sports participation (Parkkari, et al., 2004). In the Health 2000 study, approximately two-thirds of the 18 to 29 year-old responders reported taking part in leisure time sports activities two or more times a week (Koskinen, 2005). In Finnish conscripts, the person-based incidence of hospitalised injuries is close to 100 per 1000 conscripts annually, whereas the event-based incidence of musculoskeletal injuries leading to a military primary care visit is reported to be approximately 10 to 40 times higher (Heir, T. & Glomsaker, 1996; Mattila, et al., 2006; Taanila, et al., 2010). Lower limb injuries comprise a significant

(17)

portion of all musculoskeletal injuries (Almeida, et al., 1999; Heir, T. & Glomsaker, 1996; Mattila, et al., 2007; Mattila, et al., 2006; Smith & Cashman, 2002).

6.2 Epidemiology of Knee Injuries in Young Adults

6.2.1 Overall Incidence of Knee Injuries

Of the all physical activity-related injuries, knee injuries comprise approximately 15% in Finland (Haapasalo, et al., 2007). A study of sports injuries in the general population in Finland revealed that the knee was the most commonly injured body part, accounting for approximately 12.5% of all sports-related injuries in men and 17% in women (Parkkari, et al., 2004). In the national victimisation survey of 2009 (Haikonen & Lounamaa, 2010), the most commonly injured body part during sports was the ankle (26% of the sports injuries), followed by the knee (17%) and back (9%). In other leisure time activities, the knee was injured most often (25%), followed by the ankle (13%). In the US army and in Norwegian conscripts, knee injuries comprise approximately 25% of all injuries (Almeida, et al., 1999; Heir, T. & Glomsaker, 1996) and similar results are reported in Finnish conscripts for knee and shin injuries combined (Mattila, et al., 2007). At sports injury clinics, knee injuries may account for up to 40% of all injuries (Majewski, et al., 2006).

Knee pain is also a common complaint. In the Health 2000 Survey, 8% of males aged 18 to 29 and 6% of females reported knee pain in the preceding month (Koskinen, 2005). The difference between the sexes was not statistically significant. In a UK population, the prevalence of knee pain in males between 16 to 44 years was reported to be 15%, of which about 16% was disabling and 7% intense and disabling (Webb, et al., 2004). The prevalence of knee pain and osteoarthritis, which is a main reason for knee pain, increases with age in both sexes (Kaila-Kangas, 2007).

Accurate injury incidence rates of knee injuries in young adults are still unknown, especially in Finland. Knee injuries are most common in those under 30 years of age and especially in males (Gianotti, et al., 2009; Kannus & Järvinen, 1989; Majewski, et al., 2006). Kannus and coworkers studied the incidence of knee injuries in Finnish community health centre patients in the 1980s (Kannus & Järvinen, 1989). In their prospective study of 148 patients, the cumulative incidence of knee injuries was 11 cases per 1000 persons during a 1-year study period. Most of the injuries occurred between the ages 10 to 39, but the incidence rates for different age groups were not reported. Ten percent of the visits led to surgical consultation. The study population was older than the mean age of the general population in Finland. In Denmark, the cumulative incidence of acute knee injuries treated in emergency departments at the primary health care institutions is 13.3 per 1000 inhabitants annually in males and 9.7 in females (Nielsen & Yde, 1991). Not

(18)

all knee injuries in the area were treated at the same institution and only injuries less than 24 hours old were included, which lowered the reported incidence rate. Also, two-thirds of the patients were classified as having a contusion or distortion, which may have caused only minor morbidity. In the US in 2000, a markedly lower cumulative annual incidence rate of less than 3 acute knee injuries requiring a physician’s attention per 1000 persons annually was reported (Yawn, et al., 2000). Men aged 25 to 29 had a peak incidence of approximately 6 injuries per 1000 persons per year. The lower cumulative incidence rate may be due to differences in inclusion criteria, a smaller number of sports-related injuries in the US population, or even differences in insurance policies that may decrease the capture of mild injuries in the US study (Yawn, et al., 2000). In Finnish conscripts, the event-based incidence of knee disorders leading to a visit to the garrison clinic is reported to be approximately 730 cases per 1000 person years with a mean of two health care visits per knee disorder (Taanila, et al., 2010). Another report of the same study group showed that 35% of the knee disorders at the garrison clinics are acute injuries (Taanila, et al., 2009). Based on these data, the patient-based incidence of acute knee injuries treated as outpatients in garrison clinics are estimated to be as high as 130 cases per 1000 person-years. Most of the above-mentioned studies reported injuries only according to anatomical location (knee); did not describe specified injury diagnoses, or included nonspecific diagnoses such as knee sprains, strains, or contusions (Kannus & Järvinen, 1989; Taanila, et al., 2010; Yawn, et al., 2000); or the study methodology led to a clear underestimation of the injury incidence rate (Nielsen & Yde, 1991). Also, rather than reporting exact person-time (i.e., first admission due to knee injury, death, or moving out of the area as a censoring event), investigators usually reported the cumulative annual incidence, which assumes that the person is at risk for the whole study period (Kannus & Järvinen, 1989; Nielsen & Yde, 1991; Yawn, et al., 2000) and leads to a minor overestimation of time at risk and thus lowers the incidence rate.

To our knowledge, there are no comprehensive studies in the literature reporting the accurate incidence rates of knee injuries needing inpatient care in general and according to specified diagnoses in the young adult population.

6.2.2 Incidence and Relative Frequency of Common

Specified Knee Injuries and Anterior Knee Pain

The National Institute for Health and Welfare collects statistics from all outpatient visits to the special health care clinics in Finland and the most common main diagnoses are reported on a yearly basis. In the latest report from the year 2009, 28,035 patients were included in the diagnosis group S80–89 (injury of knee or shin). Of these, diagnosis code S83 (dislocation or distortion of the knee joint or ligaments) was applied to 8127 patients. A main diagnosis of M23, internal derangement of the knee, including old meniscal tears, was applied to 10,964 patients. A main diagnosis of M22, patellar diseases, was applied

(19)

to 2579 patients (Forsström & Pelanteri, 2011). Majewski and coworkers (Majewski, et al., 2006) studied the epidemiology and relative frequency of knee injuries in sports. Knee sprain without clearly identifiable internal derangement was the most common injury reported. The most commonly identified internal knee derangement was an ACL tear (20.3%), followed by a medial meniscal tear (10.8%), chondral lesion (10.6%), MCL tear (7.9%), contusion injury due to direct trauma (5.5%), lateral meniscal tear (3.7%), and patellar dislocation (3.3%). Also, a few lateral collateral ligament injuries (1.1%) and PCL injuries (0.65%) were reported. In acute knee haemarthrosis patients, the most common arthroscopic finding was ACL injury (45% of patients), followed by patellar dislocation (23%), MCL or meniscal rupture (23% each), chondral lesions (18%), and PCL rupture (3%) (Sarimo, et al., 2002). The most common nontraumatic knee disorder in young adults is AKP (Devereaux & Lachmann, 1984; Sanchis-Alfonso, Vicente, 2011).

Most ACL injuries occur during sports (Gianotti, et al., 2009). In the Finnish adolescent and young adult population, the injury incidence rate for hospitalisations due to cruciate ligament injuries is reported to be 1 per 1000 person-years for males and 0.3 per 1000 person years for females (Parkkari, et al., 2008). A slightly higher incidence rate in this age group is reported for surgically-treated ACL injuries in the general population of New Zealand (Gianotti, et al., 2009). For all age groups, the cumulative incidence rate for ACL surgeries was only 0.4 per 1000 persons annually. The injury incidence rate was highest among young adult males in their early thirties, reaching 1.6 cases per 1000 persons annually. In females, the peak incidence occurred in the late thirties: 0.8 cases per 1000 persons annually. The study is limited, however, in that the number of nonsurgically treated ACL injuries was not reported. In a US population of all ages, the incidence rate for ACL injuries treated at the orthopaedic knee injury clinic was 0.4 per 1000 persons annually (Miyasaka, et al., 1991). The incidence rate included only those injuries with pathological anteroposterior motion in physical examination. In a general population-based UK study, the cumulative person-population-based incidence of ACL ruptures treated at the orthopaedic trauma unit was markedly lower, 0.08 per 1000 persons annually (Clayton & Court-Brown, 2008). Both inpatient and outpatient care were taken into account and the age of the patient ranged from 12 to 89 years. The cumulative incidence was highest in males aged 20 to 29 years, nearly 0.4/1000 persons per year, and declining rapidly after that. In females, the age-related incidence curve was similar, but peak cumulative incidence was clearly lower, less than 0.1/1000 persons per year. The overall male to female ratio was 76/24. It must be noted that many of the patients were referred to a knee surgeon instead of the clinic involved, leading to an underestimation of the incidence rates.

The reported cumulative incidence rates in primary health care emergency department patients in Denmark are only 0.4 for isolated or combined acute cruciate ligament injuries per 1000 inhabitants per year for males and 0.2 for females (Nielsen &

(20)

Yde, 1991). Only injuries less than 24 hours old were included, which lowers the incidence reported.

Posterior cruciate ligament injury typically occurs in car collisions when the shin forcefully strikes the dashboard or during sports when a player falls forcefully on the flexed knee (Moore & Dalley, 2006). Patients are usually young adult males (Schulz, et al., 2003). Posterior cruciate ligament and posterolateral corner injuries are frequently combined with other ligamentous injuries (LaPrade, et al., 2007). Isolated PCL injuries are present in 5% of the knee injuries with acute knee haemarthrosis (LaPrade, et al., 2007). The accurate population-based incidence of PCL injuries is not known. In a study by Mattila and co-workers (Mattila, et al., 2008), PCL injuries constituted less than 10% of all cruciate ligament injuries in Finnish conscripts. Similar results were reported in Denmark (Nielsen & Yde, 1991), suggesting that the cumulative incidence of acute PCL injuries leading to a primary health care visit within 24 hours of injury might be as low as 0.02 cases per 1000 inhabitants per year. The cumulative person-based incidence of PCL injuries with associated pathologic anteroposterior motion was approximately 0.04 per 1000 persons annually in the US (Miyasaka, et al., 1991). Only those PCL injuries that were repaired were reported in the UK study mentioned above (Clayton & Court-Brown, 2008). The clearly underestimated incidence was only 0.005/1000 persons annually. The male to female ratio was 83/17 and the incidence was highest in males in the second or third decade, and declined thereafter (Clayton & Court-Brown, 2008).

Meniscal tears may represent as many as 15% of all sports-related knee injuries and 25% of all knee injuries requiring surgery (Majewski, et al., 2006). Slightly more than one-third of meniscal tears include associated ACL injury. This occurs most commonly in males aged 21 to 30, whereas solitary meniscal tears are most common in those 31 to 40 years of age (Poehling, et al., 1990).

A cumulative incidence of 0.24 to 0.27 meniscal tears per 1000 persons annually was reported at orthopaedic clinics in the UK and US (Clayton & Court-Brown, 2008; Miyasaka, et al., 1991). The overall male to female ratio in a UK study was 75/25 and the incidence was highest in young adult males, declining after the third decade. The prevalence of asymptomatic degenerative meniscal tears was high, as much as 6%, in older populations, which may, among other factors, lower the reported incidence rate (LaPrade, et al., 1994; Negendank, et al., 1990). Higher incidence rates are reported in primary health care emergency department patients in Denmark where the corresponding incidence for males is 1/1000 persons per year and for females 0.6/1000. This is also considered a possible underestimate. In Finnish primary health care, meniscal tears are reported to account for 20% of all knee injury visits, which can be recalculated to correspond to a cumulative annual person-based incidence of 2 cases per 1000 persons (Kannus & Järvinen, 1989). The highest person-based incidence rates reported are from the garrison clinics of Norwegian military conscripts, approximately 15.6 cases per 1000 person-years (Heir, T. & Glomsaker, 1996).

(21)

Traumatic chondral lesions of the knee are common in physically active young adults. Detected injuries are not always reported as a separate diagnosis, and the incidence rates and localisations are not well known (Kiviranta & Vasara, 2004). Curl and coworkers examined 31,516 knee arthroscopies, and chondral lesions were found in 63% of the patients with the mean age of 43 years (Curl, et al., 1997). The male to female ratio was 62/38. The prevalence of osteochondritis dissecans in performed arthroscopies was 0.7%, articular fractures 1.3%, grade I chondral lesions 28%, grade II 28%, grade III 41%, and grade IV 19%. Sarimo and coworkers arthroscopically examined 320 consecutive knee haemarthrosis patients in Turku University Hospital and found that 18% of the patients had chondral lesions. The precise incidence rate was not reported, but the mean annual incidence of acute traumatic haemarthrosis was 0.5 per 1000 inhabitants. Based on these statistics, the cumulative annual incidence of chondral lesions in traumatic knee haemarthrosis patients is approximately 0.1 per 1000 inhabitants. This assumption, however, has two severe limitations. First, only acute knee haemarthroses were included in the study and thus only a minor part of the all knee injuries requiring treatment were captured in the study. Second, these knee injuries were treated at the university hospital and not all haemarthrosis patients of the area were treated there.

Acute dislocations of the patella typically occur in young adults (Atkin, et al., 2000). Redislocations are common (Mäenpää, et al., 1997). The incidence of primary traumatic patellar dislocations in Finnish young adult male conscripts is 0.77 per 1000 person-years (Sillanpää, et al., 2008). In the US, the cumulative incidence rates of acute first time patellar dislocations (also nontraumatic) for Kaiser Foundation health plan members in the second decade of life are 0.3 cases per 1000 persons annually for females and 0.3 for males. In the third decade of life, the annual incidence rates are reported to be 0.09/1000 for females and 0.14/1000 for males (Atkin, et al., 2000). In the general population of Denmark, the annual incidence of patellar dislocations is 0.2/1000 inhabitants for males and 0.5/1000 for females. It must be taken into account that the US numbers are based on patients visiting a knee injury clinic and the Denmark study did not include all injuries in the study area. Of these, the study of Sillanpää and coworkers is the most generalisable to the general population of Finnish young adult males without known underestimations of incidence rates.

The annual cumulative incidence of acute collateral ligament injuries leading to an immediate visit to emergency department is 1 case per 1000 Danish men and 0.5 per 1000 women (Nielsen & Yde, 1991). Of the collateral ligament injuries, MCL injuries are the most common by far. In the US, cumulative person-based incidence of collateral ligament injuries treated at orthopaedic knee injury clinics was reported to be 0.68/1000 persons annually for MCL and 0.04/1000 for LCL injuries (Miyasaka, et al., 1991). The corresponding UK incidence rates reported in 2008 were 0.05 per 1000 persons annually for MCL injuries compared with 0.002/1000 for LCL injuries (Clayton & Court-Brown, 2008). The male to female ratio was 75/25 for MCL injuries. For LCL injuries, the male to

(22)

female ratio was 100/0, but there were only 5 cases included in the study. The incidence curve for both MCL and LCL injuries was similar to PCL injuries, highest in males in the second or third decade of life, and subsequently declining.

Anterior knee pain is suggested to be the most common knee complaint in adolescents and young adults (Sanchis-Alfonso, Vicente, 2011). The multifactorial uncertain aetiology, and confusing and changing terminology makes comprehensive analysis of the condition challenging. The earliest theory was that pain was caused by CMP (i.e., patellar chondral lesions) alone. This theory was brought into question by the finding that only half of the patients with clinical symptoms show patellar chondral lesions in arthroscopy (Leslie & Bentley, 1978). Later, the term CMP was applied only when chondral lesions and degeneration of the articular cartilage of the patella were present. Since the 1970s, PFM has been the most important and widely used theory to explain the genesis of AKP and the term patellofemoral pain syndrome (PFPS) has replaced the term CMP. The PFM theory, however, represents similar problems as CMP. While some people with remarkable PFM are asymptomatic, others have AKP and normal patellofemoral alignment (Sanchis-Alfonso, Vicente, 2011). Various other knee pathologies can also cause pain to the anterior aspect of the knee and new theories have challenged the traditional views of the origin of the pain. Some of the pathological conditions most commonly linked to AKP other than PFM and patellar chondral lesions are patellar instability and synovial impingement syndrome, including pathological plicae and fat pad impingement, patellar tendinopathy, osteochondroses, iliotibial band syndrome (runner’s knee), and bursitis (Houghton, 2007; Kodali, et al., 2011; Llopis & Padron, 2007). New theories of the origins of the pain includes pathophysiological processes such as neural proliferation in the lateral retinaculum due to periodic short-term ischaemia (Sanchis-Alfonso, V. & Rosello-Sastre, 2003) or a tissue homeostasis imbalance (Dye, 2005). The tissue homeostasis theory has received widespread attention over the last few years. The basic idea behind the theory is that the knee joint is a living, metabolically active unit and normal tissue homeostasis is required for proper maintenance and healing of the tissues. Increased loading of the patellofemoral joint leads to a loss of tissue homeostasis in the surrounding innervated tissues, which causes pain. The normal knee joint can withstand a wide range of loading and maintains its tissue homeostasis. This is called the zone of homeostatic loading. Increased repetitive loading or a single loading event sufficient to cause loss of tissue homeostasis but not macrostructural damage is considered supraphysiological. When loading is increased further, it may cause macrostructural damage such as a chondral lesion or ligament rupture. This is termed the zone of macrostructural failure. According to Dye, the various pathological conditions described above can be considered together as a loss of tissue homeostasis (Dye, 2005). One of the key points of the tissue homeostasis theory is that it can explain pain in knees with normal anatomy. The tissue homeostasis theory can be considered complementary to the PFM theory. PFM may cause increased

(23)

loading to the patellofemoral joint, thus making it more susceptible to a loss of tissue homeostasis (Sanchis-Alfonso, Vicente, 2011).

PFPS can be considered only as a nonsensical replacement of the term CMP (Sanchis-Alfonso, Vicente, 2011). Abandonment of both terms, CMP and PFPS, has been proposed (Grelsamer, 2005; Sanchis-Alfonso, Vicente, 2011). Instead of CMP, the term chondral or cartilage lesion should be used with a clear description of the detected injury. AKP appears to be the most appropriate term to be used as a main heading to describe pain in the anterior aspect of the knee that may be caused by various pathological knee conditions.

The reported incidence rates of AKP are highly varied and there are no accurate statistics taking actual exposure time into account. In sports medicine clinics, AKP may comprise up to 25% of all knee problems (Devereaux & Lachmann, 1984). In athletic young adult students, AKP was reported to occur in 24 of 282 persons during a 2-year study period, but the total exposure time and incidence rates were not reported (Witvrouw, et al., 2000). Calculations based on these numbers indicate a cumulative incidence rate of up to 43 persons per 1000 persons annually. In Norwegian conscripts, the person-based incidence of overuse knee injury, such as PFPS, iliotibial band friction syndrome, and patellar tendinitis, during basic military training is reported to be more than 200 per 1000 persons annually (Heir, T. & Glomsaker, 1996). In Israeli male infantry recruits, AKP occurred in 60 (15%) of a total of 390 study subjects during 14 weeks of basic training (Milgrom, et al., 1991). Again, total exposure time and incidence rate were not reported, but the statistics presented indicate that annual cumulative person-based incidence could be as high as 573 per 1000 persons.

These statistics provide general information concerning the importance and relative frequency of knee injuries in Finland, as well as internationally. The main results are represented in Table 1. Accurate injury incidence rates of even the most common specified knee injuries in young adults remain unclear. In Finland, the incidence rates for this high-risk subgroup are available only for cruciate ligaments and primary traumatic patellar dislocations (Parkkari, et al., 2008; Sillanpää, et al., 2008). Also, many other available studies reporting the incidence of knee injuries or disorders are based on patient populations of specialized clinics and do not include all injuries from the study area (Atkin, et al., 2000; Clayton & Court-Brown, 2008), specific patient groups like athletes or military cadets (Uhorchak, et al., 2003; Witvrouw, et al., 2000), or only very specific subgroups of injuries like surgically-treated ACL tears, knee haemarthrosis, or only injuries less than 24 hours old (Gianotti, et al., 2009; Nielsen & Yde, 1991; Sarimo, et al., 2002). This makes generalisation of these results challenging and their application for clinical practice difficult.

(24)

Tab le 1 . O ve rv ie w o f t he K ne e I nj ur y I nc id en ce R es ea rc h Au th or s Co un try Sa m pl e Ag e In ju ry o ut co m e In ci de nc e of i nj ur ie s/ 10 00 / y ea r In ci de nc e o f kn ee i nj ur ie s/ 10 00 / y ea r In ci de nc e of c ru ci at e lig am en t in ju rie s/ 10 00 / y ea r In ci de nc e of m en is ca l te ar s/ 1 00 0/ ye ar In ci de nc e of c ol la te ra l lig am en t in ju rie s/ 10 00 / y ea r In ci de nc e of c ho nd ra l le si on s/ 1 00 0/ ye ar In ci de nc e of p at el la r di sl oc at io n/ 10 00 / y ea r In ci de nc e o f an te rio r k ne e pa in / 1 00 0/ ye ar Ta an ila , e t a l., 2 01 0 Fi nla nd M ale C on sc rip ts 18 –2 8 M us cu lo sk el et al dis or de rs t re at ed a s ou tp at ien ts a t t he ga rri so n c lin ic 38 33 3, 4 73 0 3, 4 NA NA NA NA NA NA M at tila , e t a l., 2 00 6 Fi nla nd M ale c on sc rip ts 18 –2 9 Ho sp ita lis ed i nju rie s 93 .7 2 NA NA NA NA NA NA NA He ir, T . & G lo m sa ke r, 19 96 No rw ay Co ns cr ipt s ( 99 % m ale ) 18 –3 0 M us cu lo sk el et al i nju rie s tre at ed a t t he g ar ris on cli nic 11 16 to 18 36 3, 4 NA (app ro xim at ely 25 % o f t he inj ur ie s) NA 15 .6 3, 4 NA NA NA 20 9 3, 4, 7 Cl ay to n & C ou rt-Br ow n, 20 08 UK Ge ne ra l po pu lat io n 12 –9 0 Vi sit s t o o rth op ae dic tra um a u nit D ue t o m us cu lo sk el et al i nju rie s 1. 06 1, 2 (M ale s 1 .6 7, fe m ale s 0 .5 2) 0. 38 1, 2 AC L 0 .0 8 1, 2 PC L r eq uir ing re pa ir 0 .0 05 1, 2 0. 24 1, 2 M CL 0 .0 5 1, 2 LC L 0 .0 02 1, 2 NA NA NA Ya wn , e t a l., 2 00 0 US Ge ne ra l po pu lat io n 17 – In itia l v isi ts t o p hy sic ian du e t o a cu te i so lat ed kn ee i nju ry NA 2. 8 1, 3 (M ale s 3 .1 (p ea k 6 .0 4), Fe m ale s 2 .4 , (p ea k 4 .2 4) NA NA NA NA NA NA Ka nn us & J är vin en , 19 89 Fi nla nd Ge ne ra l po pu lat io n NA (Pat ien ts < 90 ) Vi sit s t o p hy sic ian d ue t o kn ee i nju rie s NA 11 1, 2 NA 2 1, 2, 4 NA NA 0. 3 1, 2, 4 NA Sa rim o, e t a l., 2 00 2 Fi nla nd Ge ne ra l po pu lat io n NA Patie nt s ( 16 to 6 8) Kn ee h em ar th ro sis pa tie nt s t re at ed i n T ur ku Un ive rs ity H os pit al NA 0. 5 1, 2, 6 AC L 0 .2 1, 2, 4 PC L 0 .0 2 1, 2, 4 0.1 1, 2, 4 M CL 0 .1 1, 2, 4 0. 08 1, 2, 4 0.1 1 1, 2, 4 NA Ni els en & Y de , 1 99 1 De nm ar k Ge ne ra l po pu lat io n NA Le ss t ha n 2 4 h ou r o ld kn ee i nju rie s t re at ed at t he e m er ge nc y de pa rtm en t ( pr im ar y he alt h c ar e) NA 11 .6 1, 3 (M ale s 1 3. 3, Fe m ale s 9 .7 ) 0. 3 1, 3 (M ale s 0 .4 , Fe m ale s 0 .2 ) 0. 7 1, 3 (M ale s 1 .0 , Fe m ale s 0 .6 ) 0. 7 1, 3 (M ale s 1 .0 , Fe m ale s 0 .5 ) NA 0. 3 1, 3 (M ale s 0 .2 , Fe m ale s 0 .5 ) 0. 4 1, 3, 5 (M ale s 0 .3 , Fe m ale s 0 .5 ) Pa rk ka ri, e t a l., 2 00 8 Fi nla nd Ge ne ra l Po pu lat io n b as ed co ho rt Ba se lin e 14 –1 8, f ol low -up i n 2 00 1 19 –3 3. Su rg ica lly r ep air ed A CL inj ur ie s NA NA 0. 61 2 (M ale s 0 .9 7, fe m ale s 0 .3 0) NA NA NA NA NA Gi an ot ti, e t a l., 2 00 9 Ne w Ze ala nd Ge ne ra l po pu lat io n NA Nu m be r o f A CL su rg er ie s NA NA 0. 37 1, 3 Pe ak In cid en ce i n m ale s 1 .6 , in fe m ale s 0 .8 ) NA NA NA NA NA

(25)

Si lla np ää , e t a l., 2 00 8 Fi nla nd M ale c on sc rip ts 17 –3 0 Ho sp ita lis ed p rim ar y tra um at ic p at ell ar dis lo ca tio n NA NA NA NA NA NA 0. 77 3 NA At kin , e t a l., 2 00 0 US Ka ise r h ea lth p lan po pu lat io n NA (Pat ien ts 10 –5 9) Pr im ar y p at ell ar dis lo ca tio ns t re at ed a t th e k ne e i nju ry c lin ic NA NA NA NA NA NA 0. 07 1, 3 (P ea k inc id en ce i n m ale s 0 .3 0 an d i n f em ale s 03 3) NA W itv ro uw , e t a l., 2 00 0 Be lgi um St ud en ts t ak ing ph ys ica l e du ca tio n cla ss es 17 –2 1 De ve lo pm en t o f a nt er io r kn ee p ain d ur ing t wo ye ar s tu dy p er io d NA NA NA NA NA NA NA 42 .6 1, 2, 4 (M ale s 3 6. 4, fe m ale s 4 9. 6) M ilg ro m , e t a l., 1 99 1 Isr ae l M ale i nf an try re cr uit s NA De ve lo pm en t o f pa te llo fe m or al p ain du rin g 1 4-we ek s b as ic tra ini ng NA NA NA NA NA NA NA 57 3. 0 1, 2, 4 M iya sa ka , e t a l., 1 99 1 US Ka ise r h ea lth p lan po pu lat io n NA Kn ee l ig am en t in jur ie s tre at ed a t t he k ne e i nju ry cli nic NA 1. 24 1, 2, 4, 8 AC L 0. 38 1, 2, 4, 9 PC L 0 .0 4 1, 2, 4, 9 0. 27 1, 2, 4 M CL 0 .6 3 1, 2, 4 LC L 0 .0 4 1, 2, 4 NA NA NA 1Cu m ula tiv e a nn ua l in cid en ce 2Pe rs on -b as ed i nc id en ce 3Ev en t-b as ed i nc id en ce 4Ap pr ox im at io n/ co nv er sio n/ ca lcu lat io n f ro m t he d at a p re se nt ed 5Pa te llo fe m or al o ve ru se 6Ac ut e k ne e h ae m ar th ro sis 7Ov er us e k ne e i nju rie s i nc lud ing p at ell of em or al p ain s yn dr om e, i lio tib ial b an d f ric tio n s yn dr om e a nd p at ell ar t en din itis 8Inclu din g o nly l ig am en t a nd m en isc al t ea rs 9Inclu din g o nly l ig am en t in jur ie s w ith p at ho lo gic a nt er op os te rio r m ot io n NA = N ot A va ila bl e

(26)

6.2.3 Risk Factors for Musculoskeletal Injuries in General

Risk factor research has focused mainly on injuries as a whole rather than knee injuries or their underlying diagnoses. Low aerobic fitness as measured by running capability is considered a risk factor for injuries in studies conducted in conscripts as well as in recruit armies (Jones, et al., 1993; Jones & Knapik, 1999; Taanila, et al., 2010). Low aerobic fitness also increases the risk for medical discharge from military service in Finnish conscripts (Taanila, et al., 2011). It must be taken into account that opposite results have also been reported. In a study considering Finnish conscripts, those with excellent aerobic fitness had an OR of 1.3 for inpatient care due to lower limb injury compared with those with poor results in running tests (Mattila, et al., 2007). In Norwegian conscripts, poor running fitness seemed to be a risk factor for musculoskeletal injuries in univariate analysis, but adjusted multivariate analysis showed it to be statistically nonsignificant (Heir, T. & Eide, 1996, 1997). In addition, in the study of Jones and coworkers (Jones, et al., 1993) dealing with male US army infantry trainees, statistical significance was obtained only in univariate analysis and running test results were not included in the multivariate analysis.

Co-impairments in muscular strength tests and Cooper’s 12-minute running tests are a risk factor for musculoskeletal disorders leading to a visit at the garrison clinic as well as for medical discharge from the military service in Finland (Taanila, et al., 2011; Taanila, et al., 2010). The overall results in muscular fitness index used by the Finnish defence forces were not associated with injuries in either of these studies, and another study concerning Finnish conscripts showed that good muscular fitness increases the injury hospitalisation risk (Mattila, et al., 2007).

The association of BMI with injuries as a whole remains controversial. In Norwegian conscripts, higher BMI increased the risk for musculoskeletal injuries treated at the military primary care in one study, but not in another (Heir, T. & Eide, 1996, 1997). Two studies reported that BMI is not associated with the injuries in US army (Jones, et al., 1993; Reynolds, et al., 2000). In Finnish conscripts, a higher BMI increases risk for musculoskeletal disorders leading to a visit at the garrison clinic and for injuries requiring inpatient care (Mattila, et al., 2007; Taanila, et al., 2010), but is not a risk factor for medical discharge from the military service (Taanila, et al., 2011). Height and weight independently are not associated with the injury risk (Heir, T. & Eide, 1996, 1997; Taanila, et al., 2011; Taanila, et al., 2010). Older age seems to increase the risk for musculoskeletal injuries in young adult Norwegian conscripts in univariate analysis, but multivariate analysis showed conflicting results (Heir, T. & Eide, 1996, 1997). Other multivariate analyses reported that older age was a significant risk factor in US army trainees, but a nonsignificant risk factor in Finnish conscripts (Jones, et al., 1993; Taanila, et al., 2010). Older age is also not a risk factor for medical discharge from the military service in Finland (Taanila, et al., 2011).

(27)

6.2.4 Risk Factors for Knee Injuries and Anterior Knee Pain

The role of demographic and anthropometric characteristics as well as physical fitness as a possible risk factor for knee injuries is not well established. An overview of the available risk factor data is presented in Table 2. There are currently no data for whether factors like height, weight, BMI, or physical fitness predisposes to knee injuries in general. The overall risk of physical activity-related knee injuries is highest in the 15 to 25 year-old age group (Haapasalo, et al., 2007). The risk of disabling knee injuries among young men in the US army increases until the age of 26 years (Sulsky, et al., 2000). In general practice populations in UK, obese subjects were nearly four times more likely to report knee pain with disability than those with a normal BMI (Webb, et al., 2004). Whether knee pain was caused by injury or osteoarthritis was not reported. Other known risk factors include sports participation, and as many as half of all knee injuries may occur during sports activities (Haapasalo, et al., 2007; Kannus & Järvinen, 1989). In Finland, females have a higher risk for knee injuries in commuting activities, whereas hazard ratios are not significantly different for lifestyle activities or recreational and competitive sports. In some specific activities, such as endurance, power, and contact sports, females have a higher injury risk than men (Haapasalo, et al., 2007).

Few investigators have examined the risk factors for specific knee diagnoses. The amount of data on intrinsic, modifiable risk factors such as BMI, weight, aerobic fitness, and muscular strength in general populations is very limited. For example, there is no single study of collateral ligament tears or chondral lesions.

Data is not available regarding whether poor aerobic fitness or older age predisposes to cruciate ligament injuries in Finland or internationally. The strength of the knee flexors and extensors is not associated with noncontact arthroscopically-confirmed ACL injuries in US Military Academy cadets (Uhorchak, et al., 2003). The authors also reported that height is a nonsignificant factor in both sexes. Higher weight and BMI increases ACL injury risk in females, but are nonsignificant in males (Uhorchak, et al., 2003). In Finnish adolescents and the young adult population, BMI is not associated with cruciate ligament injuries. The data for weight, height, and muscle strength, however, were not reported (Parkkari, et al., 2008). Participation in sports is a well-known risk factor for cruciate ligament injuries in young adults (Parkkari, et al., 2008). Even if the injury incidence rate for ACL injuries is higher for men than for women in the general population (Gianotti, et al., 2009; Parkkari, et al., 2008), the injury incidence rate and risk for cruciate ligament injuries is higher for female athletes (Mountcastle, et al., 2007; Parkkari, et al., 2008; Prodromos, et al., 2007). There are also other, nonmodifiable risk factors for ACL injuries, such as a small femoral notch width and generalised joint laxity (Uhorchak, et al., 2003). Another study, however, reported that femoral notch width did not predict ACL injuries (Lombardo, et al., 2005).

To our knowledge, there are no studies describing whether the risk of meniscal tears is associated with physical fitness. In the study of Baker and coworkers, higher weight

(28)

was shown to increase the risk when acute and degenerative meniscal tears were analysed together. Height was not associated with meniscal tears. A higher BMI increased the risk for degenerative tears, but not acute tears (Baker, et al., 2002). Degeneration occurs with aging and weakens the meniscal structures, making them susceptible to injuries (Negendank, et al., 1990). No direct evidence supports an increase in the injury risk as aging progresses. Weak quadriceps muscles, mechanical deviations, and congenital abnormalities are also suggested to increase injury rates(Miller III, 2003). The risk for meniscal tears is increased among sports participants, especially those playing soccer or rugby (Baker, et al., 2002; Baker, et al., 2003).

Young adult male patients in their early twenties with deep chondral lesions have a significantly higher mean body mass and BMI and are a little older than patients with superficial lesions (Eskelinen, et al., 2004). Height was not associated with chondral lesions in that study and physical fitness data was not available. A limitation of the study, however, was that all of the patients included had arthroscopically diagnosed chondral lesions, and thus the risk factors that predispose to chondral lesions in general are not known.

Patellar dislocations often occur during sports (Atkin, et al., 2000). Mean standing limb alignment, quadriceps angle, and rotational measurements are not associated with acute patellar dislocations. Fithian and coworkers conducted a prospective cohort study in an orthopaedic knee injury clinic to evaluate risk factors for primary and recurrent patellar dislocations. The risk factors for recurrent dislocations were female sex and older age. Their study also showed that the odds for subsequent instability are 7 times higher in patients with a previous history of patellofemoral instability (Fithian, et al., 2004). Only one study described the association of modifiable risk factors such as physical fitness and BMI with primary traumatic patellar dislocations in young adult males (Sillanpää, et al., 2008). In that study, male patients with primary traumatic patellar dislocation were typically taller and weighed more than controls (Sillanpää, et al., 2008). Factors of poor physical performance, older age, and higher BMI do not increase the risk. Most of the cases occurred during sports activities and the injury mechanism was knee flexion with a tibial valgus position in more than 90% of the injuries. Concomitant injuries were detected in almost half of the cases and haemarthrosis was present in all of the knees. Service class had to be lowered in 1 of every 5 patients, indicating a remarkable inability to cope with physically challenging duties (Sillanpää, et al., 2008).

Witvrouw and coworkers conducted a 2-year prospective study of the intrinsic risk factors associated with the development of AKP (Witvrouw, et al., 2000). Anthropometric characteristics such as weight and height, as well as cardiovascular endurance measured by an ergometer test, were not associated with the development of AKP. Of the various physical fitness tests, only a decreased explosive strength predisposed subjects to AKP. Other statistically significant risk factors were shortened quadriceps muscle, altered vastus medialis obliquus reflex time, and a hypermobile patella. Another prospective

(29)

study by Milgrom et al. reported that physical fitness and muscle strength measured by 2 km running and number of push-ups and sit-ups were not risk factors for AKP in a logistic regression analysis (Milgrom, et al., 1991). Increased isometric strength of the quadriceps muscle, medial tibial intercondylar distance, weight, and height were also not associated with the injuries. According to pooled analyses in a recent meta-analysis, BMI and older age are also not risk factors (Lankhorst, et al., 2012). Although PFM plays a major role in the genesis of AKP, there is evidence that patellofemoral alignment characteristics such as the Q-angle and genu varum/valgum and foot pronation are not associated with the development of AKP (Hetsroni, et al., 2006; Park & Stefanyshyn, 2011; Witvrouw, et al., 2000). A recent systematic review confirmed that most of the earlier suggested risk factors for AKP rely on very limited evidence (Lankhorst, et al., 2012).

As mentioned above, there is extensive research concerning musculoskeletal injuries as a whole and a limited amount of research concerning knee injuries. Most of the study populations do not represent the general population and the patient sample is restricted to a special subpopulation such as elite athletes and patient catchment of a specialised clinic or voluntary recruit armies (Jones, et al., 1993; Jones & Knapik, 1999; Majewski, et al., 2006; Milgrom, et al., 1991; Sulsky, et al., 2000; Uhorchak, et al., 2003; Witvrouw, et al., 2000). The incidence and risk factor data available are therefore difficult to generalise to the general population in clinical practice.

Another limitation of the data available is that most of the studies published only took into account knee or other musculoskeletal injuries as a whole or alternatively only according to a solitary specific knee diagnosis, such as cruciate ligament tears or AKP (Baker, et al., 2002; Heir, T. & Eide, 1996, 1997; Milgrom, et al., 1991; Parkkari, et al., 2008). This limits the ability to evaluate whether the suggested risk factors are valid for all knee injuries or only for a certain knee diagnosis. There are no comprehensive studies taking knee injuries into account as a whole or according to specific knee diagnoses. Knowledge about the specific risk factors for different injuries will allow for better analysis of possible causal relationships and facilitate the development of possible preventive measures for the appropriate targets.

(30)

Tab le 2 . O ve rv ie w o f t he r is k f ac to r r es ea rc h Au th or s Co un try Sa m pl e Ag e In ju ry o ut co m e Hi gh er h ei gh t Hi gh er w ei gh t Hi gh er B M I Ol de r a ge Po or r un ni ng fit ne ss Po or m us cl e st re ng th He ir, T . & E id e, 1 99 6 No rw ay Co ns cr ipt s 18 -2 9 M us cu lo sk el et al i nju rie s t re at ed at t he m ilit ar y t ra ini ng c am ps NS 1, 2 NS 1, 2 + 1, 2 + 1 2_NS + 1 2_NS NA He ir, T . & E id e, 1 99 7 No rw ay Co ns cr ipt s 19 - 2 8 M us cu lo sk el et al i nju rie s t re at ed at t he m ilit ar y t ra ini ng c am ps NS 1, 2 NS 1, 2 NS 1, 2 + 1, 2 + 1 2_NS NA M at tila , e t a l., 2 00 7 Fi nla nd Co ns cr ipt s 18 -3 0 In jur y h os pit ali sa tio ns M ult ipl e i nju ry h os pit ali sa tio ns Lo we r l im b i nju ry h os pit ali sa tio ns NA NA NA NA NA NA + 2 2₊ 2₊ NA NA NA NA NA -2 -2 2_NS _NA Jo ne s, e t a l., 1 99 3 US M ale a rm y i nf an try tra ine es 17 -3 5 In jur ie s r eq uir ing s ick c all v isi t du rin g 1 2 w ee ks o f b as ic t ra ini ng NA NA NS 1, 2 + 1, 2 + 1 2_NA + 1, 3 NA 2 Ta an ila , e t a l., 2 01 0 Fi nla nd M ale C on sc rip ts 18 -2 8 M us cu lo sk el et al d iso rd er s tre at ed a t t he g ar ris on c lin ic a s ou tp at ien ts NS 2 NA + 2 NS 2 + 2 NS 2 + 2, 4 Ta an ila , e t a l., 2 01 1 Fi nla nd M ale c on sc rip ts 18 -2 8 M ed ica l d isc ha rg e f ro m t he m ilit ar y s er vic e NS 2 NA NS 2 NS 2 + 2, 5 + 2 NS 2 + 2, 4 Uh or ch ak , e t a l., 2 00 3 US US M ilit ar y A ca de m y ca de ts 17 -2 3 6 No n-co nt ac t a rth ro sc op ica lly co nf irm ed A CL i nju rie s NS 1, 2 NS 1, 2 (M ale s) + 1, 2 (F em ale s) NS 1, 2 (M ale s) + 1, 2 (F em ale s) NA NA NS 1, 2, 7 Pa rk ka ri, e t a l., 2 00 8 Fi nla nd Ge ne ra l P op ula tio n ba se d c oh or t Ba se lin e 1 4-18 , fo llo w-up i n 2 00 1 19 -3 3. Ho sp ita lis ed c ru cia te l ig am en t inj ur ie s NA NA NS 2 NA NA NA Ba ke r, e t a l., 2 00 2 UK Ge ne ra l P op ula tio n 20 -5 9 ar th ro sc op ica lly p ro ve n p rim ar y ac ut e m en isc al t ea rs De ge ne ra tiv e m en isc al t ea rs NS 2, 8 NS 2, 8 + 2, 8 + 2, 8 NS 2 + 2 NA NA NA Es ke lin en , e t a l., 2 00 4 Fi nla nd M ale C on sc rip ts w ith ar th ro sc op ica lly p ro ve n ch on dr al l es io n NA Ar th ro sc op ica lly p ro ve n c ho nd ra l le sio ns NS 1 + 1, 9 + 1, 9 + 1, 9 NA NA Si lla np ää , e t a l., 2 00 8 Fi nla nd M ale c on sc rip ts 17 -3 0 Ho sp ita lis ed p rim ar y t ra um at ic pa te lla r d isl oc at io ns + 1 + 1 NS 1 NS 1 NS 1 NS 1 M ilg ro m , e t a l., 1 99 1 Isr ae l M ale i nf an try r ec ru its NA De ve lo pm en t o f p at ell of em or al pa in d ur ing 1 4-we ek s b as ic tra ini ng NS 1, 2 NS 1, 2 NA NA NS 1, 2 -1, 2,1 0 NS 1,1 1 + 1, 3 W itv ro uw , e t a l., 2 00 0 Be lgi um St ud en ts t ak ing ph ys ica l e du ca tio n cla ss es 17 -2 1 De ve lo pm en t o f a nt er io r k ne e pa in d ur ing t wo y ea r s tu dy p er io d NS 1, 2 NS 1, 2 NA NA NA 12 NS 1, 2 + 1, 2,1 3

(31)

La nk ho rs t, e t a l., 2 01 1 Ne th er lan ds / m ult ina tio na l 7 p ro sp ec tiv e s tu die s ch os en f ro m t he 3 84 5 po te nt ial ly r el ev an t ar tic le s NA Re vie w o f p ro sp ec tiv e r isk f ac to r stu die s c on ce rn ing p at ell of em or al pa in s yn dr om e NS 14 NS 14 NS 14 NS 14 NA + 3,1 0 Su lsk y, e t a l., 2 00 0 US Ac tiv e-du ty e nli ste d so ldi er s 17 -5 4 Di sc ha rg e f ro m a rm y f or k ne e-re lat ed d isa bil ity NA NA NA + 2,1 5 NA NA Ha ap as alo , e t a l., 2 00 6 Fi nla nd Po pu lat io n c oh or t 15 -7 4 Kn ee i nju rie s r ep or te d b y s tu dy su bje ct s NA NA NA + 16 17 -NA NA + = I nc re as es t he r isk - = D ec re as es t he r isk NA = N ot a va ila bl e NS = N ot s ta tis tic all y s ign ific an t 1Un iva ria te a na lys is 2Mult iva ria te a na lys is 3Pu sh -u p t es t 4 C o-im pa irm en ts i n C oo pe r’s r un nin g t es t a nd m us cu lar f itn es s t es ts 5On ly f or d isc ha rg es d ue t o m en ta l h ea lth p ro bl em s 6At t he t im e o f e nr olm en t, f ol low -u p t im e 4 y ea rs 7St re ng th o f k ne e f lex or s a nd e xt en so rs 8 B ot h a cu te a nd d eg en er at ive t ea rs w er e a na lys ed t og et he r 9 in cr ea se s r isk f or d ee p c ho nd ra l le sio ns 10Kn ee e xt en sio n s tre ng th 11Nu m be r o f s it-up s 12Ca rd io re sp ira to ry f itn es s e va lua te d b y s ub m ax im al e rg om et er t es t w as N S 13Ex pl os ive s tre ng th m ea su re d b y v er tic al j um p t es t 14Po ol ed a na lys es 15Od ds r at io i nc re as ed i n w hit e E ur op ea n m en u nt il 2 6 y ea rs o f a ge a nd t he n d ec re as ed 16In l ife st yle a ct ivi tie s 11In c om m ut ing a ct ivi tie s a nd i n r ec re at io na l a nd c om pe tit ive s po rts . O ve ra ll k ne e i nju ry r isk w as h igh es t in t he a ge g ro up 1 5 t o 2 5 y ea rs .

Epidemiology and magnetic resonance imaging-based diagnostics of knee injuries and anterior knee pain in young adults